Generally, a mammography system is an X-ray imaging system for early detection of breast cancer, and is configured to obtain a two-dimensional image by transmitting a predetermined dose of X-rays to a subject's breast, and detecting an amount of the transmitted X-rays by using an image sensor.
Recently, to overcome limitations of a conventional technology using a two-dimensional image for diagnosing breast cancer, digital breast tomosynthesis (DBT) is proposed, which uses a three-dimensional image to diagnose breast cancer.
DBT is a technology configured such that an X-ray tube is rotated within a limited range of an angle to obtain two-dimensional images from multiple angles, and the two-dimensional images are reconstructed to obtain a three-dimensional tomographic image.
A conventional mammography system applied with the DBT technology is configured such that a breast compression means is disposed between an X-ray source and an X-ray detector, and radiography is performed by the breast compression means compressing a breast in the state where the breast is placed at the upper portion of the X-ray detector.
Here, since a size of a breast and density of breast tissue vary from subject to subject, a thickness of a breast varies from subject to subject when the breast is compressed by the breast compression means for radiography, whereby a maximum angle allowing the X-ray tube to be rotated to obtain a DBT angle varies according to a thickness of a breast.
For example, as shown in FIG. 1, a thickness T of a breast in FIG. 1A is thicker than a thickness T′ of a breast in FIG. 1B, whereby in order to image the entire breast with X-rays having a fixed X-ray irradiation angle, a rotation angle range of the X-ray tube in FIG. 1A is smaller than that of the X-ray tube in FIG. 1B.
However, the conventional mammography system is problematic in that since it has no means to adjust a rotation angle range of the X-ray tube according to a thickness of a breast, some subjects are exposed to radiation more than necessary.
The conventional mammography system is further problematic in that when a radiographed two-dimensional image is reconstructed to a three-dimensional image, the system may reconstruct the image including a non-subject area, whereby it may take longer to reconstruct.